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Organization - Additional Information (Detail) - USD ($)
$ in Thousands
1 Months Ended 12 Months Ended
Jun. 30, 2018
Feb. 02, 2019
Organization Consolidation and Presentation of Financial Statements [Line Items]    
Total cost of convertible note hedge transactions   $ 91,857
Cash proceeds from sale of warrants   51,021
Total cash proceeds, net of discounts upon original issuance and offering costs $ 287,800  
Discounts upon original issuance and offering costs 6,300  
Convertible Senior Notes Due 2023 [Member]    
Organization Consolidation and Presentation of Financial Statements [Line Items]    
Debt instrument, principal amount   $ 335,000
Cash proceeds from sale of warrants 51,000  
Convertible Senior Notes Due 2023 [Member] | Convertible Bond Hedge and Warrant Transactions [Member]    
Organization Consolidation and Presentation of Financial Statements [Line Items]    
Total cost of convertible note hedge transactions 91,900  
Private Placement [Member] | Convertible Senior Notes Due 2023 [Member]    
Organization Consolidation and Presentation of Financial Statements [Line Items]    
Debt instrument, principal amount $ 300,000  
Debt instrument, interest rate 0.00%  
Over Allotment Option in Private Placement [Member] | Convertible Senior Notes Due 2023 [Member]    
Organization Consolidation and Presentation of Financial Statements [Line Items]    
Debt instrument, principal amount $ 35,000